It has been found that air vibrations in the air intake system of internal combustion engines can be utilized to exert a positive influence on the charging of the combustion chambers with combustion air. Every rotation speed of the motor is assigned a certain optimal intake pipe configuration at full load in order to achieve the maximal gas dynamic additional charging effect. The internal combustion engine can generate a high torque if long and thin intake pipes are gas dynamically active in the lower rpm range but short intake pipes with a larger inner diameter are used in the upper rpm range.
As seen in German Patent DE 36 08 310 Al, a device is known for the continuous variation of the length of an air intake manifold. The air intake pipes are coiled 360.degree. around a collecting intake pipe. The collecting intake pipe is formed by a hollow cylindrical rotating body which forms an inner wall for the intake pipe surrounding it and is provided with one opening to each inner chamber of the intake pipe. Air is drawn through the intake pipes, the openings and the collecting intake pipe in the direction of the combustion chambers. By rotating the rotating body with the openings a variable intake pipe length can be obtained. A control of the quantity of air can be achieved via a throttle valve located in the collecting intake pipe. Strong air turbulence occurs in the region of the throttle valve and the openings of the collecting intake pipe, impairing the efficiency of the process. It is extremely problematic and costly to seal the collecting intake pipe against the individual intake pipes.
A comparable design can be recognized in the air intake system shown in German Patent DE 37 14 953 Al. The outer radius of the intake pipes which here also are wound around a collecting intake pipe decreases with increasing length of the flow path through the intake pipe. As a result gas dynamic effects are positively influenced in the sense described above. Here also, however, an additional throttle mechanism is necessary, contributing to turbulence of the intake air and high cost in sealing of the system.